lib: fix process.send() sync i/o regression

process.send() should be synchronous, i.e. it should block until the
message has been sent in full, but it wasn't after the second-to-last
libuv upgrade because of commit libuv/libuv@393c1c5 ("unix: set
non-block mode in uv_{pipe,tcp,udp}_open"), which made its way into
io.js in commit 07bd05b ("deps: update libuv to 1.2.1").

Commit libuv/libuv@b36d4ff ("unix: implement uv_stream_set_blocking()")
as landed in io.js in commit 9681fca ("deps: update libuv to 1.4.0")
makes it possible to restore the synchronous behavior again and that's
precisely what this commit does.

PR-URL: nodejs/node#774
Reviewed-by: Trevor Norris <trev.norris@gmail.com>

lib/child_process.js

@@ -586,6 +586,13 @@ exports._forkChild = function(fd) {
   // set process.send()
   var p = createPipe(true);
   p.open(fd);
+
+  // p.open() puts the file descriptor in non-blocking mode
+  // but it must be synchronous for backwards compatibility.
+  var err = p.setBlocking(true);
+  if (err)
+    throw errnoException(err, 'setBlocking');
+
   p.unref();
   setupChannel(process, p);
 

test/simple/test-child-process-sync-process-send.js

@@ -0,0 +1,44 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var common = require('../common');
+var assert = require('assert');
+var fork = require('child_process').fork;
+var N = 4 << 20;  // 4 MB
+
+for (var big = '*'; big.length < N; big += big);
+
+if (process.argv[2] === 'child') {
+  process.send(big);
+  process.exit(42);
+}
+
+var proc = fork(__filename, ['child']);
+
+proc.on('message', common.mustCall(function(msg) {
+  assert.equal(typeof msg, 'string');
+  assert.equal(msg.length, N);
+  assert.equal(msg, big);
+}));
+
+proc.on('exit', common.mustCall(function(exitCode) {
+  assert.equal(exitCode, 42);
+}));